FLOOD04125

• County: Statewide
• Basin: Statewide
• Title: Interim Procedures for Evaluating Scour at Bridges
• Date: 9/1/1988
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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USGS gaging station data review

A investigation of current USGS streamflow-gaging stations will be conductea
for suitability as scour sites and/or usefulness for providing information On
scour in particular geographical areas. Past records will be scanned tor
information including ratings (with special consideration given to sites Where
ratings have indicated shifting). high-water lItuurementa and notes, and
photographs of high flows at bridge sites.

QuestionnaIre design and review

A questionnaire will be designed facilitate the evaluation of file information
on bridge sites where significant scour effects have been observed. Types of
information to be evaluated include repair and maintenance reports, boring
data, and design plans. Such information is available (==)fromiat appropriate
agencies<==).

The USGS will assist in the file-information evaluation to decide what bridges
will be considered as possible sites. The USGS will visit [==>appropriate
agencies<==) to review in house data available for potential sites.
Approximately [==>??<==] bridge sites will be visited to take notes and
photographs at potential sites.

Site selection

All field and office data wIll be compiled and assessed by the USGS, and sites
will be selected and presented to [==>sponaoring agency<==) for concurren~e.
The total of [==>number<==) sites should provide reasonable coverage on the
basi" of:

1. Drainage basin sizes will range from relatively small
,to very large.

2. Sites will be located in different geographical areas of
the study area.

3. Ha~imizing the numoer of sites located at or near a streamflow-
gaging station that has instrumentation to help monitor rapid
changes of stage likely to be encountered on the smaller basins.

4. Sites will represent various types of streambed materials found
in the study area that are prone to scour.

Individual sites will be selected on the basis of the following criteria:

1. An ample supply ot sediment will cover the bedrock and piers
will not be protected with riprap.

2. 8ridge piers will be sUnple shape and locatea near the upstream
face of the bridge for ease ot measuring scour depths. Piers will
not constrict the cross-sectional flow area by more than 10 percent.

3. Flow will be parallel to the piers.